$ C = \left[\begin{array}{rrr}1 & 2 & 1 \\ 2 & 2 & 1 \\ 0 & 0 & 2\end{array}\right]$ What is $ C^{-1}$ ?
Answer: $ = \left[\begin{array}{rrr}-1 & 1 & 0 \\ 1 & -\frac{1}{2} & -\frac{1}{4} \\ 0 & 0 & \frac{1}{2}\end{array}\right]$